PROJECT SUMMARY The availability of contemporary antiretroviral therapy (ART) has changed infection into a manageable chronic disease for people living with HIV (PLWH) who have access to and are adherent with treatment. Adherence to medications for either HIV or major medical and mental health conditions is frequently suboptimal even for those with prescription coverage. Those with multiple, chronic diseases face compounded adverse consequences when they fail to take necessary medications. Prescription drug cost containment efforts may undermine long-term adherence with implications for adverse health consequences, though the body of literature is fairly limited and dated particularly in the context of HIV. Despite this understanding, plan managers, particularly states' Medicaid programs, continue to implement restrictions through a variety of utilization management strategies such as prescription cap policies, limiting the number of medications covered per month. In our recent analyses of persistence rates for ART, renin angiotensin antagonists, and metformin in HIV+ versus HIV- Medicaid enrollees, we noted lower persistence in states with restrictive prescription caps. Our long-term research goal is to ensure effective medication utilization management policies which balance budget priorities with population quality and quantity of life. The objective of this application is to evaluate the how Medicaid prescription cap policies impact the health of persons with HIV and public expenditures. We propose to study national enrollment, prescription, hospital, and medical claims data across multiple years, exploiting the adoption of, changes to, and redaction of medication caps. In particular, we will study Medicaid and Medicare enrollees with HIV to illustrate how state-based policies contribute to outcomes in this particularly vulnerable population. These natural experiments will offer significant insights into the impact of restrictive prescription policies on patients' health outcomes and public budgets. The central hypothesis is that prescription caps will lead patients with HIV to greater rates of HIV and non-HIV chronic disease complications, leading to additional costs. The rationale for this hypothesis is that people with HIV frequently have co-occurring conditions likely to require several prescriptions simultaneously and capping the number they receive each month may undermine their health. We have already made a large investment in and established extensive experience with Medicaid claims data from 14 high HIV prevalence states (2001- 2012). Through the addition of three more years of Medicaid claims (2013-2015) and the inclusion of Medicare Parts A, B and D claims from ~300,000 HIV infected beneficiaries across the country from 2006-2015, we will have a comprehensive infrastructure from which we can describe the impact of prescription caps on ART adherence, evaluate the impact of prescription cap policies on adherence to medications for major comorbid conditions (i.e., diabetes, cardiovascular disease, serious mental illness), and estimate the potentially avoidable health and economic effects of ART and chronic disease medication adherence.